Geochemical changes in Eastern Canadian lake sediment cores spanning the last ∼150 years highlight a relative shift towards increased metals and erosive materials

Since the start of the Industrial Revolution, the chemical cycling of numerous elements has been fundamentally altered. Using Pb-210-dated sediment cores from 37 Eastern Canadian lakes situated in 4 ecozones, we quantified the geochemical change experienced across this region since ca. 1850 CE using high-resolution computed X-ray Tomography and micro-X-ray fluorescence (mu-XRF) ITRAX scanners. Independent calibrations of mu-XRF ITRAX intensities using ICP-MS and-AES found strong correlations for numerous elements. Using relative abundance measures and absolute concentration estimates, we observed that most of our study lakes recorded temporal enrichments of metals, with several sites exceeding Canadian sediment quality guidelines. Using principal component analysis, we identified that parameters commonly associated with erosion (strontium and titanium), organic matter (molybdenum incoherence to coherence scattering ratio), and metals (zinc and lead) were key variables structuring within and among-lake variation since ca. 1850 CE. Calcium was identified as an additional variable, particularly for lakes in the Mixedwood Plains (MWP) ecozone, which may be linked to catchment activities including land-use changes. Temporally, many lakes shifted towards greater accumulation of inorganic sediment, coeval with higher Pb and Zn concentrations, reaching maxima ca. 1970 CE before decreasing rapidly. These results suggest that most lakes in the region were subjected to environmental pollution but that controls on key atmospheric pollutants in North America were effective across a large part of the country.